Coating resins which have hitherto been used for the exterior finishing of buildings, motor cars, industrial machines, metal furniture, household electric furnishings/ plastics, etc., are mainly melamine resins such as alkyd melamine and acryl melamine or two-part type urethane resins.
Of these resins, melamine resins have such problems that harmful formalin is generated at curing and the cured coating is inferior in acid resistance and is liable to be corroded by acidic rain.
Also, with a two-part type urethane resin, there is a problem relating to the toxicity of isocyanate compounds used in the resin.
For solving the aforesaid problems, the inventors have investigated vinylic polymers having a silicon atom bonded to a hydrolyzable group (hydrolyzable silyl group) for coating compositions. As a result thereof, it was found that the aforesaid vinylic polymer could solve the aforesaid problems and give a curable coating resin having excellent weather resistance (JP-A-63-132977) (the term "JP-A" as used herein means an "unexamined published Japanese patent application").
On the other hand, there is a trend toward regulating the total amount of solvents generated during the application of a coating composition, e.g., the VOC (volatile organic compound) regulation of the United States.
The feature of the vinylic polymer having a hydrolyzable silyl group is that the silyl group is hydrolyzed by moisture in air and the polymer is cured through a condensation reaction. Also, since the polymer is cured while forming a stable siloxane bond, the cured coating is excellent in chemical resistance and weather resistance as compared with a melamine resin such as acryl melamine or alkyd melamine, or a two-part type urethane resin.
Moreover, when a vinylic polymer having a hydrolyzable silyl group is used as a finishing coating composition for motor cars, there are the following four problems.
First, the external appearance which is most important for a finishing coating composition for motor cars is not always satisfactory.
Second, since the curing reaction largely depends upon humidity, curing reaction under a low humidity is delayed.
Third, with the polymer alone, it is difficult to form a high solids coating which meets the VOC regulation of the United States.
Fourth, as a finishing coating composition for motor cars, the impact resistance is not always sufficient.